Creammonkey works almost exactly like every Firefox-er's favorite user-script tool, Greasemonkey. Just click the user script and select install; the script's functionality should be readily available. While many Greasemonkey scripts will work with Creammonkey, not all scripts are compatible. For example, my favorite Greasemonkey script, the Gmail Macros script, doesn't seem to work with Creammonkey. On the other hand, several that I tried did work, so YMMV.